The invention relates to an arrangement for detecting the tire Pressure of wheels of a vehicle.
The idea of measuring the tire pressure of moving vehicles has existed in the literature since 30 years. During this time, dozens of patent proposals have been made known, though none of them found wider application. These failures were due on the one hand to the overly complex sensors, efficacious at best for laboratory duties, and on the other hand to the inadequate electronic evaluation and computing facilities which could not process the great data incidence fast enough.
Through the statistical evaluation of vehicle accidents it has been shown in Britain for example that 16% of the serious accidents occurred due to insufficient pressure in at least one of the wheels. In the USA, long-distance haulage firms have begun pumping up one tire of each twin pair with up to 30% overpressure, so that the rolling resistance is reduced and transport costs cut. However, the road surface is worn unduly by this, necessitating substantial repairs.
For both cases--underinflation and overinflation of the tire--metrologies are needed for revealing such offending vehicles in moving traffic and enabling them to be eliminated. Compared with the state of the art, using equipments measuring the tire pressure for laboratory purposes chiefly and hence moving slowly, much more is demanded nowadays by insurance companies, road maintenance authorities and traffic control centers. The measuring arrangement must be transferred from the protected laboratory atmosphere to the rigorous environment of motor roads and filling stations.
The state of the art is defined in U.S. Pat. No. 5,445,020 of Dec. 2nd 1993, describing a multiple arrangement of force measuring cells installed in a flat plate system, which may be laid anywhere as a mobile measuring mat for example, especially before filling stations. This mat has square force introduction elements arranged in several successive rows.
Also known from U.S. Pat. No. 5,461,924 is a tubular transducer with force introduction and force transmission flanges, which as sensors have a number of piezo-elements that may be connected singly or in groups. While this arrangement is able to register the individual pressures of twin tire, it cannot register several measuring points on the same tire owing to the cross-talk between individual neighboring measuring elements due to the rigid tube construction.
For a relative comparison between the individual wheels of a vehicle, a measuring arrangement is known from U.S. Pat. No. 4,630,470. Here the individual wheels are excited artificially to vibration, from which a frequency spectrum is recorded. By comparing the spectrums of the individual wheels, a wheel whose pressure deviates from the others is revealed by a changed frequency spectrum. This arrangement presupposes that the majority of the vehicle's wheels are inflated to the correct tire pressure, otherwise underinflated or overinflated tire cannot be identified.
The invention is therefore based on the need for a measuring arrangement allowing the exact tire contact surface to be determined with the isobars of each wheel, representing it arithmetically and comparing it with the other wheels. For this measuring and calculating operation a large number of overrunning segments, typically 10 at least, must be sensed for each wheel.
This task is fulfilled by the invention characterized in the claims, whereby for example the contact rail laid ahead serves to ascertain the vehicle's speed in conjunction with a measuring rail, and the division of the sensor into individual elements prevents cross-talking between neighboring measuring elements, while the dimensions of the rectangular elements ensure that the measuring rail registers the measured values of the wheel rolling over it even with widely differing tread patterns.
The data acquisition facility stores the individual tire contact surfaces at once temporarily, and compares special features of the isobar patterns with the tread prints of the other vehicle wheels. Since, however, the isobar patterns of heavy goods vehicles, which inflict the greatest damage upon the roads and also cause the most serious accidents generally, are very similar and comparable with each other regardless of the make or type of vehicle and/or tires, the isobar patterns may also be compared with the image of a "normal pressure" isobar for the particular vehicle stored in the data acquisition facility, which may be derived for example from the axle load detected at the same time and/or from the number of wheels or axles passing over the installation.
A pictorial presentation or an eliminate signal is available immediately after passage. Here the processing speed must be so high that vehicles with incorrect tire pressures can be taken out of normal road traffic. In this way, traffic monitoring by tire pressure states becomes possible.